1. Field of the Invention
This invention relates to a catalyst for .alpha.-olefin polymerization. More particularly it relates to a titanium halide catalyst component supported on a magnesium compound, and a catalyst system containing such a component.
2. Description of the Related Art
As to magnesium-containing, supported type catalysts, those having a highly catalytic activity and a superior stereospecificity have been developed, and it has been well known that they are suitable for gas phase .alpha.-olefin polymerization since the catalyst residue in the resulting polymer therefrom can be easily treated and amorphous polyolefin (App) component is not required to be removed.
Further, in order to effect a good operability, it has been sought for the catalysts for gas phase .alpha.-olefin polymerization that they have a good particle shape, a narrow particle size distribution, a superior shatter resistance, etc.
As a process for improving the catalyst particle shape, Japanese patent application laid-open No. Sho 63-54405 discloses a process of dissolving a magnesium compound in an alcohol in the presence of carbon dioxide, followed by treating the solution with a mixture of a titanium halide with an organosilane to effect precipitation, adding a cyclic ether compound to effect redissolution and recrystallization and thereby obtain a carrier having a good shape, and activating it to obtain a catalyst.
In the case of gas phase .alpha.-olefin polymerization, many copolymers have been produced making use of a specific feature that the copolymer components are not dissolved off in solvents, etc., differently from the case of liquid phase polymerization, In the case where an adhesive polymer having a high content of copolymer components is produced, it is necessary that the particle diameter of the polymer powder is large for well keeping the fluidity of them so that a catalyst having a large particle diameter has been sought in order to obtain such a powder.
to well keep the fluidity of the polymer powder and hence it is necessary that the particle diameter of the polymer powder is large so that a catalyst having a large particle diameter has been sought in order to obtain such a powder.
In general, in the case of catalyst particles prepared according to a process of deposition from a solution, even when the carrier particles constituting the catalyst particles are neat and have a sharp particle size distribution, it has not been avoided that a part of the particles collapses at the subsequent activation treatment step, etc. Further, the larger the particles, the easier their collapse. Japanese patent application laid-open No. Sho 63-54405 discloses that when the particle diameter becomes as large as about 30 .mu., the quantity of the particles collapsed increases during the activation treatment with titanium halide, etc. and fine particles increase. Thus, improvement in this respect has been left behind.
The present inventors have made extensive research in a process for particularly improving the particle shape and the particle size distribution of particles having a large particle diameter, when the particle diameter of the above catalyst system is controlled over from a small one to a large one, while retaining the high activity and the high stereospecificity of the catalyst system. As a result, we have achieved the present invention according to which it is possible to obtain a supported type catalyst of large particles having a sharp particle size distribution and an adjusted particle size while preventing the particle shatter during the steps of the catalyst production.